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The Daye district represents one of the largest concentrations of skarn deposits in eastern China. There are two major types of skarn deposits (Fe skarn vs. Cu skarn) within this district, both genetically related to late Mesozoic high-K calc-alkaline granitoids. In this study, we present in situ compositional and Sr-Nd isotopic investigations of apatite from granitoids associated with Fe skarn and Cu skarn deposits to put constraints on the magma source, evolution, and volatile composition, which provide significant new insights into the genesis of the two contrasting mineralization styles in the Daye district. Apatite from granitoids related to Cu skarns and Lingxiang Fe skarn has [epsilon].sub.Nd(t) values of - 8 to - 4, similar to that of the contemporaneous mafic rocks in the Daye district, which were dominantly derived from an enriched lithospheric mantle source. Apatite in granitoids associated with the Chengchao Fe skarn has lower [epsilon].sub.Nd(t) values of - 15 to - 9, suggesting larger degrees of contaminations from ancient lower crust materials. Fractionation models based on apatite Sr/Y and Eu/Eu* ratios, suggest that magmas related with the Cu skarns have experienced amphibole-dominated fractionation under high pressure and hydrous conditions, whereas those associated with Fe skarns have undergone plagioclase-dominated fractionation at relatively low pressure and dry conditions. Based on results of apatite compositional analysis and apatite-melt partitioning data, the estimated magma Cl contents for the Fe skarn range from 3260 to 13,940 ppm, significantly higher than those for the Cu skarn (Cl = 430-5990 ppm). Apatite from Fe skarn-related intrusions has (.sup.87Sr/.sup.86Sr).sub.t ranging from 0.7073 to 0.7082, whereas the variety from Cu skarn-related intrusions displays lower (.sup.87Sr/.sup.86Sr).sub.t of 0.7054-0.7061. These Sr isotope data, combined with whole-rock S isotopes of this study and previous investigations suggest that the Fe skarn-related intrusions have assimilated larger amount of evaporite-bearing carbonate during magma ascent and emplacement. The assimilation process may have not only promoted magmatic water exsolution but also provided sufficient amount of Cl.sup.- and [Formula omitted], which facilitated effective complexation and transportation of Fe.sup.2+ and subsequent oxidization of ferrous Fe to precipitate magnetite, respectively. We suggest that evaporite assimilation into the granitoid magmas has played a crucial role in the large-scaled Fe skarn mineralization in the Daye district. This study highlights that apatite is a sensitive petrogenetic-metallogenic indicator for granitoids and thus can be useful in mineral exploration., Author(s): Run-Jie Zhou [sup.1], Guang Wen [sup.1], Jian-Wei Li [sup.1], Shao-Yong Jiang [sup.1] [sup.2], Hao Hu [sup.1], Xiao-Dong Deng [sup.1], Xin-Fu Zhao [sup.1], Dai-Rong Yan [sup.3], Ke-Tao Wei [sup.4] [sup.5], [...]

The Hongqiling magmatic Ni-Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic-ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low Ti[O.sub.2] (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg (#) (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic-ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic-ultramafic intrusions and the calculated 'trapped liquids' for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic-ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic-ultramafic intrusions formed in a post-collisional extensional environment.Le gisement magmatique de sulfures a Ni-Cu de Hongqiling, situe a la bordure sud de la ceinture orogenique d'Asie centrale (COAC), renferme plus de 30 intrusions mafiques-ultramafiques. Ces intrusions mineralisees sont constituees principalement d'harzburgite, de lherzolite, de websterite, d'orthopyroxenite et de norite (gabbro). Les mineraux constituants sont l'olivine, le diopside, la bronzite, la hornblende calcique, le plagioclase et le spinelle, l'orthopyroxene etant un mineral dominant dans ces intrusions. Ces intrusions mineralisees ne sont pas des complexes de type alaskien. Le spinelle et le clinopyroxene presentent tous deux des compositions chimiques differentes de celles de complexes de type alaskien. Les roches qui composent les intrusions ont de fortes teneurs en MgO (moyenne = 25,20% en poids) et de faibles teneurs en Ti[O.sub.2] (moyenne = 0,58% en poids). Les fortes teneurs en MgO des mineraux et le Mg (#) eleve (71) de la composition calculee du magma en equilibre avec l'olivine demontrent que le magma parental des intrusions mafiques-ultramafiques de Hongqiling etait un magma tholeiitique riche en Mg. Ces intrusions et les [much less than]liquides pieges[much greater than] qui ont produit les cumulats a olivine et orthopyroxene sont tous enrichis en elements lithophiles a grand rayon ionique et appauvris en elements a forte liaison atomique. Les valeurs de Ce/Pb, Ta/La, Th/Yb et (La/Sm)PM et l'appauvrissement en Nb et Ta donnent a penser que le magma a subi une contamination crustale. Les intrusions mineralisees de Hongqiling partagent de nombreuses similitudes avec les intrusions mafiques-ultramafiques formees dans un milieu d'extension post-collision dans la partie ouest de la COAC (p. ex. Huangshanxi), dont leurs compositions sur roche totale et la chimie de leurs mineraux. La combinaison de ces resultats et de l'evolution du segment est de la COAC nous porte a croire que les intrusions mafiques-ultramafiques de Hongqiling du Trias tardif se sont formees dans un milieu d'extension post-collision. [Traduit par la Redaction], IntroductionA number of small Ni-Cu ore-bearing mafic-ultramafic intrusions occur in the southern part of the Central Asian Orogenic Belt (CAOB); examples include the Kalatongke (Song and Li 2009; Z.C. Zhang [...]

The Yangtze Platform preserves relatively thick carbonate successions and excellent fossil records across the Ediacaran-Cambrian boundary interval. The intensely studied Meishucun section in East Yunnan was one of the Global Stratotype Section candidates for the Precambrian-Cambrian boundary. However, depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified. The Laolin section located in NE Yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the Precambrian-Cambrian boundary. However, the stratigraphic framework and correlations were controversial. We studied and systematically sampled the Laolin section and present here new carbon isotope data for this section. The Laolin section consists of, in ascending order, the Baiyanshao dolostone of the Dengying Formation, the Daibu siliceous dolostone, Zhongyicun dolomitic phosphorite, lower Dahai dolostone and upper Dahai limestone of the Zhujiaqing Formation, and the black siltstone of the Shiyantou Formation. Our data reveal a large negative [delta][sup.13]C excursion (-7.2 [per thousand], L1') in the Daibu Member, which matches the previously published data for the Laolin section, and a large positive excursion (+3.5 [per thousand], L4) in the Dahai Member, which was not shown in the published data. The excursion Ll' correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in Siberia and Mongolia. Similar magnitude excursions are also known from Morocco and Oman, for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 Ma, thus confirming a global biogeochemical event near the Ediacaran-Cambrian boundary. Our data also indicate that deposition was more continuous at the Laolin section compared with the Meishucun section, where there are no records of a comparable negative excursion near the Ediacaran-Cambrian boundary, nor any comparable positive excursion in the Dahai Member. Therefore, the Laolin section has proven potential to be a supplementary Global Stratotype Section for the Ediacaran-Cambrian boundary on the Yangtze Platform. Keywords: C-isotope stratigraphy, Ediacaran-Cambrian boundary, Laolin section, Yangtze Platform.

The Neoproterozoic mafic rocks in western Hunan, South China, form a NNE-striking mafic rock belt for which outcrops are found predominantly in Guzhang, Qianyang and Tongdao. Samples from Qianyang and Tongdao yielded ion microprobe U--Pb zircon ages of 747 [+ or-] 18 Ma and 772 [+ or-] 11 Ma, respectively. The mafic rocks are geochemically divided into two subtypes. Ultramafic rocks from Tongdao are depleted in Nb and Ti, with decoupled Nd--Hf isotopes, and geochemical features similar to the c. 761 Ma mafic--ultramafic rocks from Longsheng, northern Guangxi. Their [[epsilon].sub.Nd](t) value is -2.91, implying an enriched mantle source. Alkaline mafic rocks from Qianyang and Guzhang have high values of Ti[O.sub.2], total alkali, some high field strength elements and [(La/Yb).sub.N], and low Zr/Nb, La/Nb, Sm/Nd and [[sup.143]Nd/.sup.144]Nd ratios as well as coupled Nd--Hf isotopes. They are geochemically similar to ocean island basalts and show fractional crystallization of Fe--Ti oxides, olivine and pyroxene in the mafic magma. The c. 760 Ma mafic rocks in western Hunan may be the products of post-orogenic magmatism. After the Jinningian (Sibao) orogenic process, the upwelling of the deep asthenospheric mantle caused by the break-off and detachment of the subducted oceanic slab led to extension in the area. The extension might have taken place earlier in the Tongdao and Longsheng areas, which led to the partial melting of the lithospheric mantle that had been metasomatized during early oceanic subduction to generate a relatively large amount of sub-alkaline rocks. However, the less alkaline mafic rocks in Qianyang and Guzhang might have been generated in the relatively later stage of the extension, and may have resulted from a small degree of partial melting of the asthenospheric mantle. Keywords: mafic rocks, petrogenesis, post-orogenic extension, Neoproterozoic, South China.

Two suites of granitoids, the Late Jurassic (158 [+ or -] Ma) Linglong suite and the Early Cretaceous (130-126 Ma) Guojialing suite, crop out in the northwestern Jiaodong Peninsula, eastern China. The Linglong suite is a monzogranite, comprising alkali feldspar, plagioclase, quartz and Ferich biotite. The Guojialing suite includes at least five plutonic bodies of both granodiorite and monzogranite. The rocks are composed of plagioclase, alkali feldspar, quartz, Mg-rich amphibole and Mg-rich biotite. Both the Linglong and Guojialing suites have adakitic affinity. They are enriched in LREE with high La/Yb ratios and show positive Eu anomalies. The rocks are also enriched in LILE and depleted in HFSE with high Sr/Y ratios. The Linglong granite shows very uniform Sr-Nd isotopic compositions with initial [sup.87]Sr/[sup.86]Sr ratios of 0.7119-0.7126 and [[epsilon].sub Nd]end (T) values of -21.3 to -21.6, which are similar to those of the local Neoarchaean basement. The Guojialing suite has variable initial [sup.87]Sr/[sup.86]Sr ratios (0.7108-0.7120) and [[epsilon].sub.Nd] (T) values (-10.8 to -17.2), which are distinct both from those of the Neoarchaean basement and from those of the local enriched lithospheric mantle inferred from the coeval mafic dykes in the studied area. Detailed petrological and geochemical data indicate that the Linglong suite was derived by partial melting of Neoarchaean metamorphic lower-crustal rocks at depth of > 50 km with a eclogite residue, whereas the Guojialing suite was formed by the reaction of delaminated eclogitic crust-derived melt with the upwelling asthenospheric mantle. The petrogenesis of these two contrasting adakitic granitoids suggests intensive lower-crustal delamination during Early Cretaceous times, following a crustal thickening process from the late stage of the Early Jurassic to early stage of the Late Jurassic with crustal thickness of < 32 km to > 50 km, respectively. Keywords: granitoid, adakite, crustal thickening, delamination, Jiaodong Peninsula.

A late Mesozoic belt of volcanic-intrusive complexes occurs in Southeast China. The Qianlishan granites are distributed in the northwest of the belt. The pluton is composed of porphyritic biotite granite (153 Ma) and equigranular biotite granite (151 Ma) and was intruded by graniteporphyry dykes (144 Ma) and mafic dykes such as lamprophyre and diabase (142 Ma). The granitic rocks, consisting mainly of K-feldspar, plagioclase, quartz and Fe-rich biotite, have Si[O.sub.2] contents of 72.9-76.9%, and are enriched in alkalis, rare earth elements (REE), high field strength elements (HFSE) and Ga with high Ga/Al ratios, but depleted in Ba, Sr and transition metals. Trace-element geochemistry and Sr-Nd isotope systematics further imply that the Qianlishan granitic magmas were most probably derived by partial melting of Palaeo- to Mesoproterozoic metamorphic lower-crustal rocks that had been granulitized during an earlier thermal event. These features suggest an A-type affinity. The Qianlishan lamprophyre and neighbouring coeval mafic dykes (Si[O.sub.2] = 47.9-53.8 wt %) have high MgO and compatible element contents. These rocks also have high [K.sub.2]O contents and are enriched in alkalis, light REE, large ion lithophile elements, and depleted in HFSE. They have low initial end values and relatively high initial [sup.87]8r/[sup.86]Sr ratios. We suggest a subduction-modified refractory lithospheric mantle (phlogopite-bearing harzburgite or lherzolite) for these high-Mg potassic magmas. The Qianlishan diabases (Si[O.sub.2] = 48.4-48.7 wt %) are alkaline and have high Ti[O.sub.2] and total [Fe.sub.2][O.sub.3] contents, together with the positive initial [[epsilon].sub.Nd] value, suggesting derivation from fertile asthenopheric mantle (phlogopite-bearing lherzolite). A back-arc extensional setting, related to subduction of the Palaeo-Pacific plate, is favoured to explain the petrogenesis of the Qianlishan granites and associated mafic dykes. Between 180 and 160 Ma, Southeast China was a continental arc, forming the 180-160 Ma plutons of the late Mesozoic volcanic-intrusive complex belt, and the lower-crust was granulitized. Since 160 Ma the northwestern belt has been in a back-arc extensional setting as a consequence of slab roll-back, resulting in the lithosphere thinning and an influx of asthenophere. The upwelling asthenosphere, on the one hand, induced the local lithospheric mantle to melt partially, forming high-Mg potassic magmas, and on the other hand it underwent decompression melting itself to form alkaline diabase magma. Pulsatory injection of such high-temperature magmas into the granulitized crustal source region induced them to partially melt and generate the A-type magmas of the Qianlishan granitic rocks. Keywords: A-type granite, mafic dykes, back-arc extension setting, Qianlishan, SE China.

We report here Sm and Nd isotope data for hydrothermal tourmalinites and sulfide ores from the giant Sullivan Pb-Zn-Ag deposit, which occurs in the lower part of the Mesoproterozoic Purcell (Belt) Supergroup. Whole-rock samples of quartz-tourmaline tourmalinite from the footwall alteration pipe yield a Sm-Nd isochron age of 1470 [+ or -] 59 Ma, recording synsedimentary B metasomatism of clastic sediments during early evolution of the Sullivan hydrothermal system. Data for variably altered (chloritized and/or albitized) tourmalinites from the hanging wall of the deposit, which are believed to have formed originally ca. 1470 Ma, define a younger 1076 [+ or -] 77 Ma isochron because of resetting of Sm and Nd isotopes during Grenvillian metamorphism. HCI leachates of bedded Pb-Zn ore yield a Sm-Nd isochron age of 1451 [+ or -] 46 Ma, which is consistent with syngenetic-exhalative mineralization ca. 1470 Ma; this age could also reflect a slightly younger, epigenetic hydrothermal event. Results obtained for the Sullivan deposit indicate that the Sm-Nd geochronometer has the potential to directly date mineralization and alteration in stratabound sulfide deposits that are not amenable to dating by other isotope methods. Keywords: Sm-Nd geochronology, tourmalinites, Pb-Zn ores, Sullivan deposit, British Columbia.

The cause of the most marked changes in the evolution of life, which define the first-order stratigraphic boundary between the Precambrian and the Phanerozoic eon, remains enigmatic and a highly [...]